Through Hole PCB Assembly Guidelines

In the PCBA industry, there are three main component assembly technologies: THT, SMT and hybrid assembly. Among these, THT assembly is the oldest and most reliable technology. It is particularly suitable for plug-in components and large-volume components. The process involves inserting component pins into plated through holes on the printed circuit boards, creating electrical connections between the components and the board. This article TechSparks will provide a comprehensive guide including how to assemble, assemble design rules and why THT technology!

Through Hole Assembly Process

Manual Assembly

Manual through-hole PCB assembly

Commonly used in hobbyist or prototype projects, where component pins are inserted into through holes manually, and strong solder joints are formed through soldering. For simple boards, starting from schematic design and going through the entire board manufacturing process manually can bring joy to hobbyists. In prototype manufacturing, speed and accuracy are crucial, and manual assembly can expedite the project progress by eliminating the need for automated through-hole assembly programming.

However, manual through hole assembly has its limitations. It is not suitable for mass production, and ensuring product consistency and high quality can be challenging. Human factors, such as fatigue or lack of experience, may lead to project delays. Additionally, for larger DIP components like LED resistors and chip packaging, automatic insertion machines may not be practical.

Automatic Assembly

Automated through-hole PCB assembly

The advanced AI plug-in machine is utilized to achieve automated through-hole assembly. In this process, multiple machines work in tandem, while a technician monitors the entire process on the monitor to prevent errors. The machines used in the assembly line include:

  • PCB loader
  • Mounter
  • Solder Paste Printer
  • Chip component inspection machine
  • Reflow oven
  • Conveyor belt
  • AI plug-in machine
  • Wave Soldering Machine
  • Automatic detection equipment

Features of THT Technology

  • Robust and Reliable: Robust and Reliable: Because the pins of the components are inserted into the through holes and firmly welded through the high-temperature soldering process, there will be no problem of falling off even in the face of high vibration and shock applications.
  • Fast Turnaround: Unlike DIP components, which require skilled operators for manual assembly due to the small and dense pin pitches of SMD components, through-hole PCB assembly involves simple insertion and soldering of pins.
  • Special Requirements: Some components, such as high-capacity electrolytic capacitors, high-voltage components, power inductors, high-current components, high-power resistors, and relays, still require THT technology due to specific design requirements.
  • Expensive: One of the reasons why through hole assembly is abandoned is because manufacturers need to drill holes and then plate them in the PCB manufacturing process, which adds extra time and labor, resulting in higher costs.
  • Restrictions: Restricted: When faced with high-density circuits, the flexibility of circuit layout will be greatly affected. Firstly, large-sized components lead to more space for wiring; secondly, the height of through-hole components is much higher than that of patch components; finally, the focus of through hole assembly is via connection, which may occupy wiring space and limit the selection of wiring paths.

Through Hole Assembly PCB Design Rules

Thermal Pads

Thermal connections are a required feature of solder pads. These connections involve three or four printed wiring boards connected on pads in a plus or multiply pattern, usually on a plane layer or solid copper foil area. The actual PCB often have a spoke-like appearance on its outer surface, resembling the spokes of a bicycle.

The purpose of these radial parts on the pad is not only to connect the plane or three-dimensional copper foil area with the copper and the hole wall but also to reduce the heat dissipation effect of the copper foil area. To achieve this, the parallel ratio between the printed board copper and component lead metal requires soldered through hole to have a limited copper area while still maintaining enough area to carry current effectively. Consequently, the combined spoke widths must equal the pad diameter.

The thermal pad shares the same diameter as the other internal pads. The area, which includes the pad and spoke, is known as the thermal outer diameter, and its distance is equal to the inner diameter times 1.5.

Performance Level

The relevant IPC standards have established three generic product levels to address various PCB assembly requirements in terms of complexity, functional performance, and testing/inspection. These product levels, also known as classes, play a crucial role in guiding the design and material selection process based on the specific grade requirements.

  • Tier 1: This level encompasses consumer products, certain computers, and computer peripherals, as well as electronics used in applications where reliability is not critical, and appearance is not a primary concern.
  • Tier 2: The second level involves electronics that require high performance and extended service life. This includes communication equipment, complex business machines, sophisticated instruments, and military equipment. While uninterrupted service is expected, occasional failures may be tolerated in this category.
  • Tier 3: At the highest level, we find critical commercial and military products and equipment. These items demand an extremely high level of reliability, and any downtime due to failure is unacceptable.

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